The airway epithelium plays a central role in normal host defense and in the pathophysiology of common respiratory diseases including asthma, chronic obstructive pulmonary disease, and cystic fibrosis. Airway epithelial cells undergo dramatic changes in phenotype and gene expression in response to a wide range of relevant stimuli, including allergens, infectious agents, and pollutants. The molecular mechanisms that regulate gene expression in these cells are complex and incompletely understood. The central - hypothesis of this project is that micro-RNAs (miRNAs) contribute to the regulation of airway epithelial gene expression during normal differentiation and allergic and inflammatory responses. miRNAs are small non-coding RNAs that interact with target sequences on messenger RNAs (mRNAs) resulting in decreased mRNA stability and/or translation. Although almost nothing was known about miRNAs until the last decade, there is already abundant evidence that miRNAs can regulate the expression of thousands of genes and that miRNAs play crucial roles in development, cell differentiation, and inflammatory and immune responses. This project has two specific aims. The first aim is to determine which miRNAs are expressed in airway epithelial cells and how miRNA expression changes during differentiation and in response to IL-13, a cytokine that plays a central role in asthma. The second aim is to determine how airway epithelial cell gene regulation is influenced by effects of miRNAs on mRNA stability and translation. These experiments will make use of powerful and innovative approaches such as genome-wide miRNA arrays and a novel high throughput reporter system for analysis of miRNA activity. The work will provide new information about the expression and function of miRNAs in airway epithelial cells and may suggest new therapeutic approaches for asthma and other airway diseases. RELEVANCE: Asthma is a common inflammatory disease with significant morbidity and mortality. The mechanisms underlying inflammation and airway remodeling remain incompletely understood, and are likely influenced by a variety of regulatory factors within airway epithelial cells. By studying changes in the airway epithelium during allergic and inflammatory stimulation, we may find new targets for therapeutic interventions for asthma, as well as other common inflammatory lung diseases such as chronic obstructive pulmonary disease and cystic fibrosis.